The matrix isolation technique has been combined with infrared spectroscopy and theoretical calculations to characterize the products of the photochemical and thermal reactions of cyclopentadiene, cyclopentene, cyclopentane, and cyclopropane with CrCl2O2. While initial twin jet deposition of the reagents led to no visible changes in the recorded spectra, product bands were observed following irradiation with light of lambda > 300 nm. The irradiation was shown to lead to oxygen atom transfer to the five-membered rings, forming complexes between cyclic alcohol derivatives and CrCl2O. For the cyclopentadiene and cyclopentene systems, complexes between cyclic ketone derivatives and CrCl2O were also observed. For cyclopropane, a ring-opening oxidation reaction followed by fragmentation was observed for the first time, forming the H2C=O-CrCl2O complex and C2H4. In the room temperature thermal (merged jet) reactions between CrCl2O2 and cyclopentadiene, cyclopent-3-enone was observed. At the higher temperatures, 150 and 200 degrees C, 1,3-cyclopentanedione was also observed as well. No product bands were detected in the merged jet experiments for the other three systems. These conclusions were supported by isotopic labeling (H-2) and by B3LYP/6-311G++(d,2p) density functional calculations.